Hull balsa core replacement advice

To the laminate schedule question.

If you are using epoxy it makes no difference what was there originally, if the new laminate is the same thickness as the original laminate it will be stronger. The fabrics used with epoxy are only the structural type, no CSM, which made up a good portion of the old laminate.

 

Lotsa good advice, I only differ in a few ways.

1. The first consideration is scrapping the boat. Sorry, but unless the boat is worth more than 20k USD, it ain’t worth fixing unless you love love it.

2. Epoxy is more foolproof, but can’t be used under gelcoat afaik. Consider using epoxy putties (epoxy and cabosil) to bond the balsa to the inside laminate. You might want to get a 2 hour tropical epoxy from Systems 3. A two hour window will close quickly. The work underneath is horribly difficult and worse if pushed to 30 minutes due to weather. All epoxy putty must be troweled onto a hawk thin to extend work time and keep from sunshine. One hour epoxy in 90 degree heat will kick too fast for most amateurs.

3. Bonding upside down is an absolute nightmare. Work in small sections less than 2’ wide. Consider vacuum bagging the core bond work. The bag can leak a bit, but the up pressure will save your brain from melting. I wish you’d have opened the inside instead, but that ship has sailed. @Rumars has given you solid advice on how to bond the balsa using the plastic sheet over a barrel method. But you could also use scrim foam, more money, no rot, less rigid to impact. I would recommend you hotcoat the sanded substrate (inside skin) by rolling a 2’ section then let it kick. Use a 1/8” or 2-3mm vee trowel and apply cabosil and epoxy in a ratio of a bit over 2:1 by volume over the neat coat. The mix should not deform under trowel. It will use a LOT! Mix the batches in a 1/2 gallon container with 12oz super slow epoxy and 26 oz (by vol) cabosil. Then apply your balsa core which has been prefilled and wetted. If no vac, you can use two people and hotglue holdup jigs to the hull. Make these in advance to allow for core/no core margins. The two hour resin is your friend. It will postcure in hot weather and if it prints through; who cares?

4. Burn test your outside laminate yourself. Don’t breathe the fumes! Take a picture of the discrete layers and we can probably tell you what you have if your pieces are say 6” sq.

5. For the exterior skin; return with polyester or ve and use the same skin as original or close. Then you can gelcoat final. The skin layup also sucks because it wants to fall off. Presand the balsa and prewet it with resin. You can table wetout smaller pieces on plastic, aluminum foil, and then the stack. Lift with 2-3 people, anchor the end and then press on the plastic until the wetted skin is well adhered. Everyone needs to be in a tyvek hooded suit for the lift. Use 2” or 50mm overlaps on skins and mechanical key days to days. Make sure to use a fin roller for consolidation, hands are not good enough. Consider vac bagging this part as well.

This job sucks, so pay attention to diseconomy. Noone will pay you for the repair when you sell the boat. The work has no value except to you.

For the repair, epoxy putty around ingress areas will crack if laid up over 1/2” thick by 1/2” thick. You will be able to put a large bond around the ingress area, but do it in a couple goes or it’ll fail (crack) and always allow space for sealant as well.

For you workspace, use butyl vac bag tape to hang a 3-6mil plastic drape around the area. Last thing you can afford is rainwater ingress. All I have for now.

 

Moisture meters are cheap. less than $20. I wouldnt risk laying up without it giving how much you are going to spend.